1. Field of the Invention
The invention relates to photographic film processing, and more particularly, concerns an improved method and doctoring surface conformation for depositing a thin uniform layer of processing fluid on a moving run of a photographic film strip.
2. Description of the Prior Art
As a result of recent developments in the motion picture art, motion picture systems have been devised in which exposure, processing and projection operations are carried out on a photographic film strip contained at all times in a multipurpose cassette. Such a system has been disclosed in several U.S. patents, assigned in common with the present invention. In these cassettes a supply of light sensitive film can be exposed in a camera adapted to receive and operate the cassette. Processing or developing of the exposed film to provide the conventional series of positive transparent image frames is achieved by merely placing the cassette in a player or processing and viewing apparatus capable of activating a processor contained in the cassette. During the processing mode, the exposed film is rewound and a coating or layer of processing fluid from the processor is deposited along the length of the film. After processing in this manner, the player apparatus is operated as a projector to advance the film incrementally, frame-by-frame, past a light source. As a result, the scenes to which the film were exposed are capable of being reproduced on a screen.
While the advance in the motion picture art represented by such a system is apparent and needs no elaboration herein, it is critical to satisfactory performance of the system that the processing fluid must be deposited uniformly within extremely small dimensions over the emulsion layer on the film during processing. Failure to achieve such a uniform processing fluid layer on the emulsion layer can result in undesirable blemishes, sometimes observable as streaks during projection of the processed film. It follows, therefore, that the achievement of a uniform layer or coating of processing fluid on the film during the processing operation has been a major focal point of attention in overall system development.
The current state of the art with respect to achieving a uniform coating of processing fluid on such cassette contained film strips is represented by the disclosures of U.S. Pat. No. 3,871,013 issued Mar. 11, 1975 to Edward F. Burke and Douglas B. Holmes, and U.S. Pat. No. 3,951,530 issued Apr. 20, 1976 to Frank M. Czumak, Paul B. Mason and Joseph A. Stella, both of which patents are commonly assigned with the present invention. In the disclosures of these patents, an inclined doctoring surface is used to develop a positive hydrodynamic force in the deposited processing fluid traveling therepast to thereby hold the film in engagement with an underlying pressure pad. To provide a net balance of forces on opposite sides of the film, the pressure pad is operative to support the film beneath the doctoring surface.
Entry of foreign particles, such as dust, into the cassette interior may arise from a number of factors, and in particular arises by virtue of ventillation openings in the cassette. While the presence of such particles in themselves is not a serious problem to film strip exposure and projection, it is critical to proper film strip processing that foreign particles present on the film strip be prevented from accumulating in the region of the doctoring surface by which the processing fluid is spread uniformly onto the film strip. The achievement of a net balance of forces on opposite sides of the film strip as it passes the doctoring surface in accordance with the disclosure of the aforementioned issued U.S. patents has contributed substantially to the solution of this problem by permitting film strip carried particles to pass the doctoring surfaces without accumulation and without dragging or streaking the processing fluid in a manner to create blemishes which will appear in the viewed images of the processed film strip. There still remains, however, some potential for wedging and accumulation of foreign particles as a result of the narrow gap between the doctoring surface and the film strip.
Moreover, the problems of achieving a uniform layer or coating of processing fluid on the film strip during the processing operation are further compounded by the requirement that each cassette carry its own processor and that the cassette and its components including the processor must be capable of mass production manufacturing techniques and be within tolerance levels incident to such techniques for the system to be acceptable in a competitive commercial market. Accordingly, the structural organization of the means by which the processing fluid is distributed onto the film and the successful elimination of disturbances on coating uniformity caused by trapped particles is critical to the overall system in which the cassette is used.